The tool-head supporting structure of this invention is primarily adapted and pre-eminently suited for use with machine tools such as transfer machines and the like. In these types of machine tools, the conventional practice is to mount the tool heads that come in usually from one or both sides of each work station to perform a machining operation such as drilling, tapping or chamfering, for example, on work in the station. The tool head is carried by a saddle that is mounted for reciprocation on raised parallel ways surmounting a bed or base disposed alongside the station. Many machining operations require that the feed motion of the tool head be limited precisely and the usual practice is to provide a fixed stop on the bed or base against which the saddle or a movable stop carried thereby butts at the extreme forward limit of its travel. Retraction of the saddle on the ways to move the cutting tools away from the work usually is controlled by a limit switch in the control circuit of the machine.
Manifestly, a considerable amount of foreign matter, such as chips, metal shavings, and the like, is created in each work station by the machining operation performed therein. A certain amount of this scrap material invariably falls on the bed and ways ahead of the saddle, and sometimes it lodges between the fixed and movable stops and prevents the saddle from advancing as far as it is intended to go and therefore prevents the intended machining operation from being performed properly. For example, if the tool head is drilling a blind hole that must be cut precisely to a predetermined depth, a chip or shaving lodged behind the fixed stop will prevent the saddle from contacting the stop with the result that the hole is not drilled to the desired depth. As a consequence, the workpiece is defective and may have to be scrapped; or worse yet, it may cause serious damage to the tools or tool carrying and actuating mechanisms in one or more subsequent work station of the machine.
Most machines of the type with which the present invention is adapted to be used are equipped with chip disposal systems, and efforts have been made to prevent random chips and shavings accumulating ahead of the saddle from interfering with the reciprocatory motion of the latter or with the machining operation. However, considerable difficulty has been experienced in clearing away this material due in considerable degree to the form of the base and way structure that supports the saddle. The saddle conventionally is reciprocally actuated by a motor-driven feed screw that extends through a running nut on the saddle. The feed screw and its drive motor are mounted on the base with the screw below the saddle between and parallel to the ways on which the saddle travels. This arrangement has required that the ways stand relatively high off the base in order to accommodate the feed screw and related mechanism and this in turn created a relatively deep, open topped channel between the ways in which chips tended to collect and from which the chips were difficult to remove. A typical prior art structure of this type is shown in FIG. 2 of the Van den Kieboom U.S. Pat. No. 3,213,711 dated Oct. 26, 1965 and assigned to the assignee of the present invention. This prior construction made it difficult to keep the drive components and the stops as well as the ways free of chips and other foreign matter that sometimes interfere with easy operation and precise positioning of the saddle and the cutting tools carried thereby. Also, the position of the feed screw between the ways and substantially below the saddle has on occasion placed excessive strain on the working parts due primarily to the relatively great spacing between the screw and the spindle-driven cutting tools. Further, when the nature of the machining operation is such that relatively heavy loads are imposed on the saddle and its actuating mechanism, the forces thus created have sometimes tended to spread the high standing ways and to warp the saddle supporting structure.